The goals of the current proposal are to define the relationship between growth hormone (GH)/insulin-like growth factor-I(IGF-1) and immune system function in elderly adults, and to determine whether GH therapy can enhance immune function in this population. Aging is accompanied by a decrease in GH/IGF-I production and decrease in T-cell numbers and function, as well as T-cell regulatory processes. These changes in immune function may impact on the increased incidence of certain infections (tuberculosis, herpes zoster, pneumonia) as well as cancer in this age group. This proposal is designed to test the hypothesis that elderly adults with GH deficiency will have decreased immune system function which will be restored to normal by GH therapy.